(1) Field of the Invention
The present invention relates to towing devices and more particularly tow cables with vibration damping means.
(2) Brief Description of the Prior Art
For towed components such as arrays or streamers, strum (vortex-induced vibration) is a persistent problem. Such vibration is transmitted into the towed array or streamer, causing damage to internal components.
The prior art includes a number of patents addressed to the management of such forces in cables.
U.S. Pat. No. 5,214,244 to Cummings et al., for example, discloses an underwater cable having a flexible, elongated core surrounded by a flexible, elongated jacket. A distributed jacket includes a helically displaced phase shifter to decouple the cable from strumming produced by shedding of von Karman vortex streets from the cable.
U.S. Pat. No. 5,601,046 to Berglund discloses a variable gap, distributed-capacitance sensor that provides an output signal that is a function of its instantaneous elongation. The sensor is integrally associated with a seismic isolator section for measuring the instantaneous stretch thereof.
It is an object of the present invention to provide a still better method for reducing strum in tow cables.
The present invention is a method for reducing strum in a tow cable extending from a marine vessel. Such cables have an adjustable length. The length of the cable is adjusted so that the number of longitudinal waves is an integral number.